In the United States alone, new brain tumors develop in nearly 2,000 children and 35,000 adults each year. Most brain tumors are primary, meaning that they rarely spread beyond the brain, as opposed to metastatic. Brain tumors can be further divided into benign tumors which grow slowly and do not spread and malignant tumors that spread and invade surrounding tissues aggressively. More adults die each year of primary brain tumors than of Hodgkin's disease or multiple sclerosis, making it the third leading cause of death from cancers (Black, New Engl. J. Med.1991, 324:1471-1476). Patients diagnosed with malignant gliomas have an average life expectancy of 36-48 weeks, and for the last several decades the survival rate has remained similar without dramatic improvement (Black, New Engl. J. Med.1991, 324:1471-1476).
Treatment of brain tumors faces a unique challenge compared to other types of cancers, due to the fact that not only are they developed within bone-covered structures (e.g., cranial cavity), thereby having restricted space to expand, but they are also embedded deeply within an organ carrying a multitude of vital functions. Therefore, even a benign tumor can be life-threatening if it is in an area of the brain that controls critical body functions such as breathing or blood circulation. Treatment normally begins with surgical resection and then follows with radiation or chemotherapy. Surgery faces the risk of removing surrounding tissues that may carry vital brain functions, while radiation and chemotherapy can both harm normal tissues that are near or along the treatment path. Indeed, if the tumor is in regions of cerebral hemispheres that control speech, vision, movement or cognition, surgery usually is not recommended. In addition, the use of radiation on children under the age of three is often prohibited because this is a critical time period of brain development. Chemotherapy, on the other hand, has been offering very limited applications, primarily attributed to the palliative response and limited duration of effects due to lack of targeting and selectivity of the drugs.
Primary brain tumors, including medulloblastoma, typically have poor prognosis in children, particularly if the primary tumor cannot be completely resected. Currently chemotherapy has done little to improve the outcomes for patient diagnosed with medulloblastoma. In addition, it recurs in a majority of patients and patients suffer significant morbidity related to current state-of-art therapeutic approaches. Hence, patients typically undergo multiple surgeries with reduced chances of survival.
Alzheimer's disease (AD) is the most common form of dementia. This incurable, degenerative, and terminal disease was first described by German psychiatrist and neuropathologist Alois Alzheimer in 1906 and was named after him. Generally, it is diagnosed in people over 65 years of age, although the less-prevalent early-onset Alzheimer's can occur much earlier. As of September 2009, this number is reported to be 35 million-plus worldwide.
AD develops for an indeterminate period of time before becoming fully apparent, and it can progress undiagnosed for years. The mean life expectancy following diagnosis is approximately seven years. Fewer than three percent of individuals live more than fourteen years after diagnosis.
Currently used treatments offer a small symptomatic benefit; no treatments to delay or halt the progression of the disease are as yet available. As of 2008, more than 500 clinical trials have been conducted for identification of a possible treatment for AD, but it is unknown if any of the tested intervention strategies will show promising results.
What is needed are additional methods of treating medulloblastoma and other cancers and central nervous system disorders such as Alzheimer's disease. Targeted treatment methods are particularly needed.